Inboard auxiliary or main drive engines which use directed water for propulsive power such as propellers and marine jets develop thrust by transfer of momentum from the ejected water to the boat. With propeller drives and submarine discharging jets, the ejected water transfers a significant percentage of its thrust back into the hull, called a "thrust deduction factor," as a result of a negative pressure turbulent wake created largely against the aft portion of the hull. The remaining thrust, or actual propulsive thrust, acts to drive the hull into equilibrium with hull resistance as the vessel accelerates to speed. The invention herein described provides a means wherein heat from the motor or engine is used to raise the temperature of the exterior boundry layer water used for thrust in a jet pump. Also, the engine or motor exhaust gases are vented around the outside of the ejected jet stream. The gases around the jet stream, as the stream leaves the boat hull at high speed, expands much easier than the jet stream, therefore substantially reducing the thrust deduction factor, and increasing net submarine discharging jet efficiency. The increase in water temperature over ambient water by the warmed pump casing increases the propensity of air to come out of solution in the jet stream, and lowers the energy required to cause the jet stream to "supercavitate" as it leaves the jet stream nozzle. This increases pump efficiency proportional to the drop in energy required and lost in passing the jet stream into supercavitating flow. To reduce parasitic hull drag and deterioration of jet efficiency by marine life growing inside the jet pump, streamlining and sealing hull closures are incorporated. These principles hold for use of the system as a conventional marine auxiliary and power plant, as well as a thrusting device such as bow and stern thrusters.